Wednesday, November 18, 2015

Understanding the glue that binds us all: the science of the future Electron Ion Collider

Abhay Deshpande (Stony Brook)

We know enough about the fundamental properties of quarks, gluons (collectively called: partons) and their interactions to be sure that QCD is the correct theory of Strong Interactions. However, when a large number of partons are put together, their collective behavior is often surprising i.e. un-understood. Gluons seem to play a central role in most of these instances. For example, despite forty years of dedicated experimental efforts around the world (CERN, SLAC, DESY, BNL & JLab) and the associated theoretical development in this field, we still do not understand how the nucleon's spin, a fundamental property of the nucleon, comes about from the collection of its constituents and their interactions. We do not yet fully understand the confinement of patrons in colorless hadrons. Do parton's angular momentum and gluon's helicity contributions have something to do with it?.We do not know yet. On the other hand, when nucleons or nuclei are accelerated to high energies, and explored with a high energy probe, a new state of universal gluon dominated matter is predicted based on experimental evidence from the high energy e-p collider (HERA) at DESY, and nuclear collisions at Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). If such a state of universal gluonic matter (the Color Glass Condensate) exists, it would be fundamentally important to explore and understand its properties. A high-energy high-luminosity electron-ion collider (EIC) with polarized beams and variable center-of-mass energy will be an ideal machine to explore these emergent phenomena and address the most compelling and yet unresolved questions in QCD. I will review the science highlights that motivate this collider and present the prospects of its realization.